Friction and wear of Si3N4 ceramics.

New ceramics such as Si3N4, SiC, PSZ, etc. are expected to be widely utilized as the wear resistant materials for bearing, mechanical seal or other sliding contact applications. For this purpose, it is essential that their tribological properties are thoroughly understood and the effects of load, sliding velocity, temperature, atmosphere and other sliding conditions on friction and wear are clarified. Since ceramics are usually fabricated through sintering process, they have a wide range of microstructures and physical properties, which should affect their tribological properties.In this paper, some mechanical properties, friction and wear of Si3N4 ceramics, fabricated mostly by pressure sintering, were measured, and their interrelations were investigated. The sliding tests were conducted between the same materials with a pin-on-disk friction and wear tester. The friction force was monitored by a load cell, and the wear volume was obtained by measuring the weight loss of the pin sample.The coefficient of friction decreased as the hardness and the fracture toughness of the sample increased. This fact may suggest that the friction force is proportional to the real contact area and is related to the fracture process at the contact point. Any relationship was hardly recognized between the specific wear rate and the hardness or the fracture toughness as a whole, but a negative correlation may probably exist for Si3N4 ceramics with MgO additives. The wear mechanism of Si3N4 ceramics was also investigated by observing the wear surfaces and wear particles with a scanning electron microscope.